In order to develop a vaccination strategy for stimulating the immune response against Human Immunodeficiency Virus (HIV), we propose to construct adenoviral vectors based on serotypes 26, 33 and 35 encoding immunogenic proteins involved in HIV infection. We and other groups have demonstrated previously in murine and non human primate models that direct vaccination with recombinant adenovirus (rAd) type 5 encoding a variety of target antigens elicits strong specific immune responses against the transgene products (see Appendix 1-4). Currently, a major limitation to rAd immunization strategies in humans is the preexistence of neutralizing antibodies directed against the most prevalent strains of the virus. A second hurdle towards the development of an effective anti-HIV DNA vaccine has been the poor expression level of HIV-encoded proteins in transduced eukaryotic cells. Interestingly, however, preliminary studies conducted in Asian and North American populations have revealed that less than 10% of tested individuals have neutralizing antibodies against adenovirus serotypes 26, 33 or 35. Moreover, we and others have been able to optimize the codon of SIV and HIV antigenic sequences, resulting in high level expression in eukaryotic cells. Hence, we hypothesize that the current technical limitations of using adenovirus type 5-based live vaccine vectors may be overcome by implementing constructs based on "unconventional" recombinant adenoviral subtypes that integrate codon-optimized HIV antigen cDNAs. We also speculate that these studies should lead to more effective vaccination strategies designed to treat acquired immunodeficency disorders.